Everyone travels differently, so I think that accounts for the weight loss, or gains.
I tend not to eat a lot on vacation, but that's also because 99% of my vacations are to warm/beach climates in which you don't really want to eat all day due to the heat, nor would you want to be bloated doing beach shit
Now on the other hand, if you're in Japan or Europe during the winter, you're probably going balls deep.